1. Field of the Invention
The present invention relates measuring instrumentation, and more particularly to a capacitive fill level measuring instrument.
2. Description of Related Art
Capacitive fill level measuring instruments (e.g., as further described in published German patent application 100 08 093, and German Patent 196 44 777) are used for capacitive detection of the fill level of liquids, bulk materials, or other fillers, etc., in a closed or open container. Such capacitive fill level measuring instruments operate under the principle that the level to be measured of the filler affects a capacitance between a reference electrode and a fill level sensor or sensor array, due to the difference between the dielectric constant of the filler and that of air.
Accordingly, such capacitive fill level measuring instruments include a power supply, an evaluation circuit, and a fill level sensor having several sensor arrays. The sensor arrays of the fill level sensor are connected to the power supply and evaluation circuit. Electrical lines are used connect the sensor arrays to a multi-pole side of a select switch and to connect a mono-pole side of the select switch to the power supply and evaluation circuit. The select switch therefore includes a plurality of terminals on the multi-pole side and one terminal on the mono-pole side, making it possible to electrically connect a selected terminal of the multi-pole side to the terminal of the mono-pole side or vice versa.
The power supply circuit supplies the necessary voltage and current to the fill level sensor and evaluation circuit. The evaluation circuit determines the level of the filler based on which of the sensors of the sensor array are still to be reached, have already been reached, are no longer being reached, etc., by the filler. The sensors of the sensor arrays of the fill level sensor can be located on top of one another, next to one another, and/or overlapping on top of one another, etc.
The select switch can employ an analog or digital multiplexer or MUX function (compare, German Patent 196 44 777) for providing a power supply function, wherein the power supply and the evaluation circuit can be connected from the terminal of the mono-pole side to one of the terminals of the multi-pole side, and an evaluation function, wherein a sensor of the sensor array can be connected via the terminal of the multi-pole side and a terminal of the mono-pole side to the power supply and evaluation circuit. Accordingly, such a select switch electrically connects a selectable terminal of the multi-pole side to the terminal of the mono-pole side and vice versa, wherein a voltage value or value proportional to the voltage value at the selected terminal of the multi-pole side appears at the terminal of the mono-pole side.
The capacitive fill level measuring instrument described in published German Patent Application 100 08 093 includes various optional measurements that can be implemented in embodiments of the present capacitive fill level measuring instrument. Further, in addition to the sensor arrays located on top of one another, on one side or both sides, there can be a matrix of horizontally and vertically running conductor paths, wherein each horizontally running conductor path is connected on one side to a sensor array and on the other side to the vertically running conductor path, the horizontally running conductor path with the vertically running conductor path to which it is connected forming an electrical line or part of an electrical line.
Capacitive fill level measuring instruments can be classified as open electronic systems, wherein the sensor surfaces of the fill level sensor cannot be completely shielded and, thus, can release electromagnetic radiation and signals into a vicinity thereof, and, conversely, can pick up electromagnetic radiation and signals from the environment, resulting in undesirable electrical interference. This is especially problematic in capacitive fill level measuring instruments, wherein the distance between the sensor elements of the fill level sensor, and the power supply and evaluation circuit can be considerable.
As noted above, capacitive fill level measuring instruments operate under the principle that the level to be measured of the filler affects the capacitance between the reference electrode and a fill level sensor or sensor array, due to the difference between the dielectric constant of the filler and that of air. However, the relative dielectric constant of air is about 1.00055, while the relative dielectric constant of water is about 80.3, and that of oil is about 2.2. Accordingly, determining the level of various types of fillers having widely varying dielectric constants can prove problematic to conventional capacitive fill level measuring instruments.
In addition, many capacitive fill level measuring instruments are not able to measure at a certain fill level the capacitance value that exists between the sensor array and the reference electrode. Accordingly, how a fill level of the filler in a container is determined using such a capacitive fill level measuring instrument will now be described.
For example, assume that the fill level sensor has a hundred sensor arrays located on top of one another, that one sensor is spatially directly adjacent to a previous sensor array, and that the fill level sensor has a height corresponding exactly to the difference between the minimum height of the filler and its maximum height, so that each sensor array is responsible for exactly one percent of the difference between the minimum height of the filler and its minimum height. Under these assumption, the following applies:
If there is no filler opposite the sensor array, not even partially, the filler has the minimum possible fill level, in any case the fill level to be minimally detected. This is defined as xe2x80x9ccontainer empty.xe2x80x9d
If there is filler opposite the uppermost sensor array over its entire height, then filler being opposite all sensor arrays, the filler has the maximum possible fill level, but in any case reaches the fill level which is the maximum to be detected. This is defined as xe2x80x9ccontainer full.xe2x80x9d
If the filler, for example, reaches exactly to the upper edge of the 51st sensor array and thus exactly to the lower edge of the 52nd sensor array, the fill level is 51% of the fill level to be detected at maximum, therefore 51% of the difference between the state xe2x80x9ccontainer emptyxe2x80x9d and the state xe2x80x9ccontainer full.xe2x80x9d
If the filler reaches, for example, exactly to the middle of the 75th sensor array, the fill height is 74.5% of the fill height which is the maximum to be detected, therefore 74.5% of the difference between the state xe2x80x9ccontainer emptyxe2x80x9d and xe2x80x9ccontainer full.xe2x80x9d
Since, as stated above, such capacitive fill level measuring instruments are not used to measure at a certain fill level the capacitance value that exists between the sensor array of the fill level sensor selected by the select switch and a reference electrode, it is generally not possible, in any case not easy, to distinguish between the state xe2x80x9ccontainer emptyxe2x80x9d and the state xe2x80x9ccontainer full,xe2x80x9d because for both the state xe2x80x9ccontainer emptyxe2x80x9d and the state xe2x80x9ccontainer fullxe2x80x9d the same measured value is determined via all selectable sensor arrays and it is unknown which measured value results from a sensor array which is not opposite the filler, and which measured value results from a sensor array which is opposite the filler over its entire height.
The manufacturers of such capacitive fill level measuring instruments often do not know which fillers will be employed in their fill level measuring instruments. If, for example, a certain capacitive fill level measuring instrument is used for determining the fill level of water, the measured value of a selected sensor array which is opposite the water is xe2x80x9crelatively large.xe2x80x9d However, if the same capacitive fill level measuring instrument is used to determine the fill level of oil, the measured value resulting from the selected sensor array which is opposite the oil is xe2x80x9crelatively small.xe2x80x9d
Accordingly, the capacitive fill level measuring instrument of the various described embodiments at least partially eliminates the aforementioned problems with the background fill level measuring instruments.
According to one embodiment, a capacitive fill level measuring instrument is provided, including a fill level sensor having one or more sensor arrays; a select switch having a multi-pole side thereof connected to the fill level sensor; and an evaluation circuit connected to a mono-pole side of the select switch. A value corresponding to a state in which a sensor array is not connected to the evaluation circuit is measured by the evaluation circuit to determine a fill level of a container.
According to one embodiment, a capacitive fill level measuring instrument is provided, including a fill level sensor having one or more sensor arrays; first and second select switches having a multi-pole sides thereof connected to the fill level sensor; and an evaluation circuit connected to mono-pole sides of the select switches. The sensor arrays are alternately connected to the multi-pole sides of the first and second select switches.
According to one embodiment, a capacitive fill level measuring instrument is provided, including a fill level sensor having one or more sensor arrays; a select switch having a multi-pole side thereof connected to the fill level sensor; and an evaluation circuit connected to a mono-pole side of the select switch. After a first fill level determination, sensor arrays adjacent to a boundary layer are one of triggered and interrogated.
Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention is also capable of other and different embodiments, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.